1. Field of the Invention
This invention relates to magnetic domain device apparatus and, more particularly, to improvements for packaging such apparatus.
2. Description of the Prior Art
The present invention provides an improvement to magnetic domain device apparatus such as, for example, the type disclosed in the publication entitled "Magnetic Bubble Module--Double Density", W. A. Lyons and A. A. Rifkin, IBM Technical Disclosure Bulletin, Vol. 15, No. 5, October 1972, page 1602.
The pluggable package disclosed in the aforementioned publication has a planar single magnetic plate which provides the bias field. Magnetic domain, also referred to as a bubble in the art, chips are mounted to the conductors of a single-sided conductor insulator carrier, i.e. Mylar (registered trademark of E. I. DuPont de Nemours & Co.). The chip-carrier assembly is in turn mounted to the magnetic plate by back bonding the carrier to the surface of the plate, there being a similar assembly also affixed to the opposite surface of the plate in the same manner. The entire assembly of chips, insulator carriers and magnetic plate is sandwiched between two parallel I/O plates and within a spacer structure which separates the two I/O plates and supports the magnetic plate. The conductors of each carrier are connected to the respective I/O plate that is located on the same side of the magnetic plate as is the particular carrier. The I/O pins of the package, which are normal to the I/O plates, are carried by the spacer structure and are interconnected to the conductors of the carriers via their respective I/O plates.
The package of the aforementioned publication has several disadvantages. For example, its mechanical and electrical connection reliability is impaired because of the number and complexity of interconnection interfaces required and/or different thermal characteristics at each interface. In particular, the interconnection interface between the chip terminals and the conductors of the Mylar carrier and the underlying interconnection interface between the Mylar carrier and the magnetic plate are subject to failure due to mechanical stresses caused by thermal cycling effects and the like. In addition, the bias field provided by the single magnetic plate requires critical centering of the chips with respect thereto because of the field distortion associated with the edges of the magnetic plate and the like, thus limiting the number of chips that can be mounted for a given area size magnetic plate.
In U.S. Pat. No. 3,864,671 there is disclosed another type of magnetic domain device package. It uses a permanent magnet ring or framelike structure for biasing the domain devices. As is well known to those skilled in the art, the framelike magnet provides a magnetic field within the opening, and it is essential that the domain device lie within the opening formed in the framelike structure and be in substantial coplanar relationship therewith. Thus, in such type packages a separate nonmagnetic substrate member is required to support the domain device and at least some of the conductors associated therewith. Thus, in the particular package disclosed in the aforementioned patent the framelike permanent magnet ceramic does not directly support the magnet domain device. Furthermore, such prior art packages of the type described, for example, in the aforementioned patent, are subject to poor mechanical and electrical connection reliability due to the number and complexity of the interconnection interfaces required and/or different thermal characteristics at each interface.
It is well known that the bias field for a magnetic domain device has to be held within a relatively controlled range. If the field strength is above the range, the bubbles collapse. If the field strength is below the range, on the other hand, the bubbles spread out and their control becomes unreliable. As is well known to those skilled in the art, both the domain device and magnetic bias field produced by the permanent magnet are temperature responsive. Because of the physical separation of the domain devices and the permanent magnet in the prior art structures, the two were subject to two different and varying temperatures. This adversely affected the thermal tracking characteristic between the two, i.e. the ability to maintain the temperature differential between the domain devices and the permanent magnet within some predetermined operating tolerance and hence within the aforementioned range. As a result of the aforementioned separation, the prior art structures were more susceptible to being inoperable because of the inability to stabilize the aforementioned temperature differential.